Dual-core comprising zero gradient center and positive gradient outer core layer

Abstract

A golf ball including an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition, and an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface. An inner cover layer is formed over the core and includes an ionomeric material. An outer cover layer is formed over the inner cover layer and includes a castable polyurea or a castable polyurethane. The first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 18 Shore C greater than the geometric center hardness to define a positive gradient outer core layer and a shallow positive hardness gradient core.

1 . A golf ball comprising
 an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;   an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface;   an inner cover layer disposed about the core, the inner cover comprising an ionomeric material and having a material hardness of about 55 Shore D or greater; and   an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a material hardness of 20 Shore D to 70 Shore D;   wherein the first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 43 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.   
     
     
         2 . The golf ball of  claim 1 , wherein the inner core has an outer diameter of about 0.5 to about 1.40 inches. 
     
     
         3 . The golf ball of  claim 2 , wherein the inner core has an outer diameter of about 0.8 to about 1.30 inches. 
     
     
         4 . The golf ball of  claim 1 , wherein the geometric center hardness is about 55 Shore C to about 82 Shore C. 
     
     
         5 . The golf ball of  claim 4 , wherein the geometric center hardness is about 60 Shore C to about 80 Shore C. 
     
     
         6 . The golf ball of  claim 1 , wherein the second outer surface hardness is about 84 Shore C to about 98 Shore C. 
     
     
         7 . The golf ball of  claim 6 , wherein the second outer surface hardness is about 84 Shore C to about 95 Shore C. 
     
     
         8 . The golf ball of  claim 1 , wherein the second outer surface has a hardness of about 2 to 43 Shore C points greater than the geometric center hardness. 
     
     
         9 . The golf ball of  claim 1 , wherein the second outer surface has a hardness of about 3 to 37 Shore C points greater than the geometric center hardness. 
     
     
         10 . The golf ball of  claim 1 , wherein the first substantially homogenous rubber composition comprises an antioxidant-to-initiator ratio of about 0.4 or greater. 
     
     
         11 . The golf ball of  claim 1 , wherein the ionomeric material comprises a Na-, Li-, or Zn-ionomer having an acid content of about 11 wt % to about 20 wt %. 
     
     
         12 . The golf ball of  claim 1 , wherein the ionomeric material comprises an ionomer having an acid content of about 16 wt % or greater and a maleic-anhydride grafted metallocene-catalyzed polyolefin. 
     
     
         13 . A golf ball comprising
 an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;   an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface;   an inner cover layer disposed about the core, the inner cover comprising an ionomeric material and having a material hardness of about 55 Shore D or greater; and   an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a material hardness of 20 Shore D to 70 Shore D;   wherein the first outer surface has a hardness of about 16 to 34 Shore C points less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of about 3 to 37 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.   
     
     
         14 . The golf ball of  claim 13 , wherein the first outer surface has a hardness of about 20 to 27 Shore C points less than a hardness at the geometric center. 
     
     
         15 . A golf ball consisting of
 an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;   an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface; and   an outer cover layer disposed about the core, the outer cover having a material hardness of 50 Shore D to 70 Shore D;   wherein the first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 43 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.